As a method for producing a highly branched polymer (a hyperbranched polymer), it is proposed a polymerization method of a monomer having two or more radically polymerizable double bonds in the presence of a radical polymerization initiator. Examples of the method include methods for producing a highly branched polymer by so-called initiator-fragment incorporation (co)polymerization that uses a divinyl compound having two vinyl groups or a dimethacryl compound having two methacryl groups and an azo polymerization initiator (see Patent Documents 1 and 2, and Non-patent Documents 1 to 3).
The previously proposed methods for producing a highly branched polymer are characterized by using a monomer having two or more radically polymerizable double bonds, and a radical polymerization initiator in an amount equimolecular or more with respect to that of the monomer. While the monomer is polymerized, the polymerization initiator generates an initiator fragment radical that reacts with a propagating terminal radical of the polymer to stop the reaction and to give a highly branched polymer that includes highly branched polymeric chains, does not include long polymer chains, and is soluble in organic solvents and the like.